late reply to my own post.
I just realised that the amount of small file generated by ID3Browse just
killed my free space. The total ID3 dir is a few kB in "reality", 3 megs
under ntfs and 190 megs under fat32...

If you search for a song tagged "Melody of time", just browse thru
id3>songs>M>mel>melody of time
No text to enter, fast browsing using rockbox "one screen scrolling"...
"songs" can exist or not, depending if you generate only playlists for
songs, or also for artists etc...
"mel" is a 3 char directory, apparently all songs in my collection starting
with "M" also started with "me"

The only "problems"
-work only for tagged mp3 (what ! you own a mp3 player and your songs aren't
tagged ;) ?)
-You have to synchronise your id3 search folder with a PC (I use a sync app
that start a .bat after the process is done)
-a bit hard to use (command line tool) but there are lots of exemples and a
gui is available. Once mastered, it's a killer app !